The interaction of platelets with the coagulation and fibrinolytic systems in the maintenance of hemostasis may become pathogenic, requiring prevention and treatment. The fibrinogen receptor antagonists of Formula I are useful in treating various diseases related to platelet aggregation and fibrin formation.
An interest in platelet inhibitors has reemerged as a result of a better understanding of the role of platelets and thrombosis in the pathogenesis of vascular disease, including unstable angina, acute myocardial infarction and stroke.
Platelets are cell-like anucleated fragments, found in the blood of all mammals, which participate in blood coagulation. Fibrinogen is a glycoprotein present as a normal component of blood plasma. Fibrinogen participates in platelet aggregation and fibrin formation in the blood clotting mechanism. Platelets are deposited at sites of vascular injury where multiple physiological agonists act to initiate platelet aggregation culminating in the formation of a platelet plug to minimize blood loss. If the platelet plug occurs in the lumen of a blood vessel, normal blood flow is impaired.
Platelet membrane receptors are essential in the process of platelet adhesion and aggregation. Interaction of fibrinogen with a receptor on the platelet membrane complex IIb/IIIa is known to be essential for normal platelet function.
Zimmerman et al., U.S. Pat. No. 4,683,291, describes peptides having utility in the study of fibrinogen-platelet, platelet-platelet, and cell-cell interactions. The peptides are described as having utility where it is desirable to retard or prevent formation of a thrombus or clot in the blood.
Pierschbacher et al., U.S. Pat. No. 4,589,881, describes the sequence of an 11.5 kDal polypeptide fragment of fibronectin which embodies the cell-attachment-promoting activity of fibronectin.
Ruoslahti et al., U.S. Pat. No. 4,614,517, describes tetrapeptides which alter cell-attachment activity of cells to various substrates. FIG. 1 lists the polypeptides that were synthesized by Ruoslahti et al. in "determining the smallest peptide exhibiting cell attachment activity". Ruoslahti et al., Pat. No. 4,578,079, describes similar tetrapeptides having Ser substituted with Thr or Cys.
Pierschbacher et al., Proc. Natl. Acad. Sci. USA, Vol. 81, pp. 5985-5988, October, 1984, describe variants of the cell recognition site of fibronectin that retain attachment-promoting activity. Pierschbacher et. al. further assayed the cell attachment-promoting activities of a number of structures closely resembling the Arg-Gly-Asp-Ser peptide, and found "that the arginine, glycine, and aspartate residues cannot be replaced even with closely related amino acids, but that several amino acids can replace serine without loss of activity."
Ruoslahti et al., Science, Vol. 238, pp. 491-497, Oct. 23, 1987, discuss cell adhesion proteins. They specifically state that "elucidation of the amino acid sequence of the cell-attachment domain in fibronectin and its duplication with synthetic peptides establish the sequence Arg-Gly-Asp (RGD) as the essential structure recognized by cells in fibronectin".
Cheresh, Proc. Natl. Acad. Sci. USA, Vol. 84, pp. 6471-6475, September 1987, describes the Arg-Gly-Asp-directed adhesion receptor involved in attachment to fibrinogen and the von Willebrand Factor.
Adams et al., U.S. Pat. No. 4,857,508, describes tetrapeptides which inhibit platelet aggregation and the formation of a thrombus.
It is, therefore, an object of the present invention to provide fibrinogen receptor antagonists for use in inhibiting the binding of fibrinogen to blood platelets and inhibiting the aggregation of blood platelets. Another aspect of the present invention is to provide novel fibrinogen receptor antagonist compounds. Other objects of the present invention are to provide methods of inhibiting the binding of fibrinogen to blood platelets and inhibiting the aggregation of blood platelets, through the administration of novel fibrinogen receptor antagonist compounds. The above and other objects are accomplished by the present invention in the manner described below.